2 phases to same box

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  #1  
Old 03-01-05, 07:28 AM
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2 phases to same box

I had my electrician run two circuits to my garage. He used 12-3 to run these two circuits using the same neutral for both since the two circuits are not connected to the same phase. As I ran the circuits to outlets around the garage, I used 12-3 from quad outlet box to box. In each box I wired one outlet pair using the red as the hot and another outlet pair using the black as the hot. I figured this would give me the flexibility to distribute the load in the garage across the two circuits simply by plugging into the left or right outlet in a box. When I described this to my father, an electrical engineer, he expressed a concern that the potential across the two circuits is 220v and because of their close proximity to each other, dangerous. But isn't this the case with any two circuits that may be adjacent and connected to different phases, which could easily be the case with the appliance outlets in my kitchen, which are all on dedicated circuits?

Is this really a concern?

TIA,

Joel
Bayside, NY
 
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  #2  
Old 03-01-05, 07:51 AM
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Your father is theoretically correct, but the risk is so low as to not be of any significant concern. To 220 volts, a quarter-inch of separation is as good as a mile. It's not going to jump that gap. I suppose that if you were to take off the cover plate and stick your hand in the box with the power on, the shock would be bigger this way. But you're not going to stick your hand in the box with the power on, so the point is moot.

A more practical concern is how you're going to provide the required GFCI protection on these circuits.

The circuit you have is called a "multiwire circuit". In different parts of the code and for different interpretations, it can be considered either one circuit or two circuits.
 
  #3  
Old 03-01-05, 08:51 AM
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You have three choices to provide the necessary GFCI protection for these receptacles.

1) Use a 240 volt GFCI breaker in the main panel where the circuit to the garage originates.

2) Use a GFCI receptacle for each and every receptacle in the garage. Connect everything to the line side of the receptacles.

3) Install 2 GFCI receptacles in the first box in the garage. Connect the incoming power wires to the line side. From this box on use 2 runs of 12-2 (or a single run of 12-4 that has two neutrals) and go from box to box, making the connections on the load side of the original GFCI receptacles. maintain the same hot-neutral pair for each receptacle.

Not that for safety and code compliance you need to have GFCI protection. Don't skip this important step.
 

Last edited by racraft; 03-01-05 at 02:23 PM.
  #4  
Old 03-01-05, 01:24 PM
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Originally Posted by racraft
2) Use a GFCI receptacle for each and every receptacle in the garage. Connect everything to the load side of the receptacles.

I believe Bob means connect everything to the LINE side of the recepticles...
 
  #5  
Old 03-01-05, 02:22 PM
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Sorry, my mistake. I did mean line side.
 
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